Rectangular pulse amplifier



March 14, 1950 Q. A. KERNS RECTANGULAR PULSE AMPLIFIER Filed March 1, 1948 I INVENTOR. Quzwrnv A KER/v5 A 7'7'ORNEK Patented Mar. 14, 1950 RECTANGULAR PULSE AMPLIFIER Quentin A. Kerns, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application March 1, 1948, Serial No. 12,356

Claims.

This invention relates to a power amplifier circuit and more particularly to a power amplifier for passin rectangular waves of voltage without distortion.

In known power amplifiers, it has been found that the reproduction from input to output of rectangular voltage waves is very poor; that is, the circuit elements introduce instability and small deformations at the input circuit are magnified to the output to round off the corners of the voltage wave and introduce ripples in the maximum value. These difiiculties are eliminated in the present invention by carefully controlling the operating voltages at the circuit elements and by the addition of circuits in the output stage to sharpen the corners and remove any ripples from the output rectangular voltage wave.

It is therefore an object of this invention to provide a new and improved power amplifier circuit.

Another object of the invention is to provide a circuit adapted to amplify rectangular pulses of voltage with a minimum amount of distortion.

A further object of this invention is to provide a power amplifier circuit having an output circuit adapted to damp transient voltages in the output circuit due to inductance.

A still further object of this invention is to provide an electronic couplin circuit wherein the screen grid of the tube is maintained at a constant potential above the cathode.

Other objects and advantages of the invention will be apparent in the following description and claims considered together with the accompanying drawing which is a schematic wiring diagram embodying the invention and is the sole drawing thereof.

Referring to the drawing in detail, an input plug H furnishes the circuit with a high positive voltage l2 (approximately +5000 volts), a medium positive voltage l3 (approximately +400 volts), a neutral connection 14 which is grounded, and a negative voltage [6 (approximately -400 volts).

A second input plug I! is connected to the control grid of a pentode tube 18 through a resistor l9. Other connections of the tube [8 are as follows: the cathode is connected to the suppressor grid by a lead 2| and to the neutral connection M by a lead 22, the control grid is connected to the negative voltage [6 through a resistor 23, the screen grid is connected to the neutral connection I4 through a by-pass condenser 24 and to the junction of two resistors 26 and 21 which divide the voltage between the positive voltage l3 and the neutral connection l4, and the anode is connected to the positive voltage I3 through a dropping resistor 28. The anode of this tube I8 is further connected to the control grid of a, tetrode type beam power tube '29 through a coupling condenser 3|. The tube 29 is further connected as follows: the cathode is connected to the negative voltage [6 by a lead 32, the control grid is connected to the junction between two resistors 33 and 34 of a voltage divider between the negative voltage 16 and the neutral connection 14, the screen grid is connected to the neutral connection 44 through a biasing resistor 36 and to the negative voltage l6 through a by-pass condenser 37, and the anode is connected to the positive voltage I3 through a dropping resistor 38. The anode of the tube 29 is further connected to the control grid of a pentode type coupling tube 39 through a limiting resistor4 I. Further connections of this tube 39 are as follows: the cathode is connected to the suppressor grid by a lead 42 and to the negative voltage [6 through a non-inductive resistor 43; the screen grid is connected to the cathode through a condenser 44 and to the cathode of a diode type tube 45, the anode of which is connected to the neutral connection [4 by a lead 46; and the anode is connected to the positive voltage I3 through an anode resistor 41. The cathode of the tube 39 is further connected to the control grid of a triode type driver-amplifier tube 48 by a lead 49. A lead BI is connected from the cathode of the tube 48 to the neutral connection I4. The anode of the tube 48 is connected, by a lead 52, to the anode of a diode type tube 53 and to one terminal of the primary winding of an output transformer 54. The second terminal of the primary winding of the output transformer 54 is connected, by a lead 55, to the cathode of the tube 53 through a parallel circuit comprising a condenser 56 and a resistor 5'5, and further to the high voltage I2. The terminals of the secondary winding of the output transformer 54 are connected to output terminals 58 and 59 of an output plug 60.

Now consider the operation of the invention with the plug l I so connected to a suitable source of direct current that the required operating voltages are impressed on the tubes is, 29, 39, 45, 48, and 53. Under this condition the circuit is operable to amplify voltages appearing at the input plug ll. Since the circuit has been designed for th purpose of amplifying rectangular pulses of Voltage, the following description will be confined to this operation. A positive rectangular pulse of voltage impressed at the input plug l1 results in a positive voltage at the control grid of the tube l8 which then becomes conductive.

The tube I8 is normally non-conductive by reason of the negative control grid to cathode voltage impressed from the negative voltage 16. Since the tube l8 conducts for the duration of 28 for a like period, thereby lowering the anode pulse of voltage is impressed from the cathode of the tube 39 on the control grid of the tube 48. This latter tube 48 is normally non-conductive because of the negative bias voltage fur- 5 nished the control grid across the resistor 43. Thus at the time-the positive rectangular pulse of -voltage appears at the control gridvof the tube 48, the tube conducts and draws maximum current through the primary winding of the output voltage and impressing a negative rectangular-@110 transformer 5Q. This output transformer 54 is of pulse of voltage on the control gridof thehpeam power type tube 29 through the coupling con- In this first stage ofvthe/ circuitrcariee denser 3 I.

apulse type having a low value of leakage reactance. The voltage developed across the primary windingzof the transformer 54- is a negative recis taken to eliminate distortiongbymontrolof'the tangular'=pulse-.which is transformed into a posiscreen grid voltage of the tube;. l8.- .Thissis accomplished with the by-pass condensenzdwhicha grounds any alternatin components of the voltage present at the screen grid, thereby maintaining the voltage substantially constant. It is also tobenoted that the combinationof.theresistors 28, 33,.and 34 and thecondenser 3.1 have ;a illrennggma to ,remove ripple voltages which are er mi zord ary powensupplies.

negativegthe control gridmore negative, and the cathode still more negative; therefore; the tube is normally; conductive with a maximum=,amount of current 7 flowing. ,Now, with a negative .reC.-. tangular .pulse ofivoltageirnpressed at-the control grid the tube vjceases to, conduct and the,- anede-- voltage. becomes s,ubstantially that I of the posi--, tive voltage] ;-T.h is positive. voltage atethe anode 1 of the "tube 323 v remains, for: the ,durationpfthe-v negative rectangular; pulse applied-;to the controls,

the input pulse of voltage.

grid, thereby reproducingan amplified image of The can lingtube 39 is connectedr the form of a cathode follower and-its COIlttOlggIid voltage;r

is .obtained directly from the anode or -tn ltu e 2 9., i This means that the tube .39.is normally non conductive and. becomes, conductive only during theitime that thelanode -13: the -tube,-,29 is ;-sufli-,

cierl tly positive to overcome the negative cathod bias voltage, which time-occurs; coincident with Y th input pulseofeyolta fi The cathode of -t l;1is, wheres therefore, furnishes a positives-pulse; off-y voltagato'the control gridnf,thedrivereamplifier tube t is-to -he noted-that connecticnsehave been-'made -inthe screen, I d circuit, of the tube 395to maintain the scree grid ataconstant p0:

tential above the cathode t a times eliminating a so'urce of distortion i, -t1- e-,,ampl ifier circuit.

The-referenced connections are; the condenser M a dv lhe diodev tube -;Q gl.-'1ll3h are connectew M series from the, ,cathode of, the 7 tube. 39 gto the neutral, connection wi,th the; screen grid con-g. nected to the,junction:betweentherrg thusdsolating; the screen grid ,irom direct connection; to the power supply. ,Since the.. anode of the,tube 45 is directly connected to the ne and the cathode is; conneeted ito. the negative r voltage lfi -through the condensenhhand hare-fer Sistor 43, e denee i ch re' d ur ne thea timethegtube-fig isnon conductive, ther y pla 1-;

resistor 43,}the voltage pulserisrapplied;to :the

maint n h 91166 r eh ufl de:vo ez-w connected'to the outputof said amplifier circuit,

constant, ,,The yalue of the capacitance ;-:of the condenser: M soechosen thatthe desired voltagezu.

cang-bec maintained for the duration of the pulse .e tube ,2}! is,.s o -.co nected,that the anode 5;

W added 'rl hewtuhe 53 and the condenser 56" are connected inseries-across the primary Winding of z' the -trans-former fi i with-the anode "of the' tube 53 connected; to the anode'of; thetube-48'. Thus-,

e15 tive rectangular-pulse of voltage across the secondary -winding offlthe transformer 54 and therefore across the two output terminals 58 and 59. Even though the transformer 54 is a low leakage reactance type, there isr still sufficient leakage '20 reactance to cause transientavoltages in the out- -connected resistorge'i and condenser 56 havebeen ,duringtheneg-ative. pulse of voltage :at the anodereturns-irons its low- -value toits normal value,

tube 5.45; tobecome more-positive than the cathode 40 then, di charges throughwthe resistor bl during the output voltagel'is prevented. if Whfleathe salientr; features of this invention n spiritandtswpefof this invention, audit is thereforennottdesired- 511101 limitthee invention to ."the

m What-risr-claimed j, voltagei at saidwathoder'landLa positive voltage :1 at said :anode, la condenser for coupling said:

cathodestosaidscreen-gridanda'diode tube hav-' m onn i n- 4 inguitganode connectedtztoia. neutral point and itscathode connected tozsaidscreen grid whereby said 'screemgridr is maintained at a constant potential above the cathode of said electron tube.

2. -In an amplifier for rectangular voltage ing a ,positive potential on sthescreen grid r. When 1-65 pulsesp the combination comprising an" amplifier" circuit havingat ileast- -two stages of amplification, a driver-amplifiercircuit, a cathode-follow- 1 e er :tube having==at least-"a cathode, control grid,

screen grid, and anode, said control grid being said cathode" being "connected tothe input of 75 said screen grid for maintaining a constant,

putm-ZE'Q damprtheqtransient positive swing of the voltage; 1 at; thegsend ofethe voltage pulse-9131161011? cuit comprising the diode tube 53sand the parallel Oflllbez'lillbe' w; the anodefiof the tube 53 is more negative tharrthe cathode and the'diode-gcannot I fire: However, as-stated above,'zwhen the voltage the; leakage: reactance causes the voltage to build up-toa value highervthan the normal value; which portion of the voltage. causes the anode of the resulting;;in,rthe tube drawing current;thereby* y g; ;,charging the condenser 56. The condenser 56:

th'eepfihiod' between pulsesh Thus, distortion of have been,describediin detailwith-respect to one embodiment ,-=-itrwill; ofrcourseybe apparent that numerous modifications imay bemade withinr the" 1 In, 'anelectronic; coupling circuit the com- ,,-binationcomprising; an-welectron-tube having at; least'g'ai-icathode, a :controlgrid, --a screen: grid," and an anode, means for impressing a negativew saidu driver 'amplifien means for-biasing said anodei positively and s'aid -cathodenegatively, a condenser connectedibetween said cathode and cathode to screen grid bias, a diode tube having its anode connected to a neutral point of said biasing means and its cathode connected to said screen grid for furnishing a charging path for said condenser, and means connected to the output of said driver-amplifier for damping transient voltages.

3. In an amplifier for rectangular voltage pulses, the combination comprising an amplifier circuit having at least two stages of amplification, a driver-amplifier circuit, a cathode-follower tube having at least a cathode, control grid, screen grid, and anode, said control grid being connected to the output of said amplifier circuit, said cathode being connected to the input of said driver-amplifier, means for biasing said anode positively and said cathode negatively, a condenser connected between said cathode and said screen grid for maintaining a constant cathode to screen grid bias, a diode tube having its anode connected to a neutral point of said biasing means and its cathode connected to said screen grid for furnishing a charging path for said condenser, an output transformer connected across the output of said driver-amplifier, means for supplying a bias voltage to said driveramplifier through the primary winding of said transformer, a diode tube having its anode connected to one side of the primar winding of said transformer and its cathode connected to the other said of said primary winding through a condenser, and a resistor connected across said condenser for discharging said condenser.

4. In an electronic coupling circuit, the combination comprising an electron-tube having at least a cathode, a control grid, a screen grid,

and an anode, means for impressing a negative voltage at said cathode and a positive voltage at said anode, a condenser for coupling said cathode to said screen grid, and rectifier means connected between said screen grid and a neutral point for furnishing a charging path for said condenser whereby said screen grid is maintained at a constant potential above said cathode.

5. In an electronic coupling circuit, the combination comprising an electron tube having at least a cathode, a control grid, a screen grid, and an anode, a voltage source having a positive terminal, a negative terminal, and an. intermediate neutral terminal, a dropping resistor connected between said anode and said positive terminal, a cathode resistor connected between said cathode and said negative terminal, a condenser connected between said cathode and said screen grid, and rectifier means connected between said screen grid and said neutral terminal to form a charging path for said condenser.

QUENTIN A. KERNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,149,361 Rath Mar. 7, 1939 2,178,985 Blumlein Nov. 7, 1939 2,273,934 Campbell Feb. 24, 1942 2,390,503 Atkins Dec. 11, 1945 2,423,671 Wolff July 8, 1947 2,444,854 Schlesinger July 6, 1948 

